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190
191<div class="main">
192
193
194
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]195<h1>The <em>Magick</em> Behind ImageMagick</h1>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]196<p class="navigation-index">[<a href="#overview">Architecture Overview</a> &bull; <a href="#cache">The Pixel Cache</a> &bull; <a href="#stream">Streaming Pixels</a> &bull; <a href="#properties">Image Properties and Profiles</a> &bull; <a href="#tera-pixel">Large Image Support</a> &bull; <a href="#threads">Threads of Execution</a> &bull; <a href="#distributed">Heterogeneous Distributed Processing</a> &bull; <a href="#coders">Custom Image Coders</a> &bull; <a href="#filters">Custom Image Filters</a>]</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]197
cristyffb69ed2010-12-25 00:06:48 +0000[diff] [blame]198
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]199<div class="doc-section">
200<p>The citizens of Oz were quite content with their benefactor, the all-powerful Wizard. They accepted his wisdom and benevolence without ever questioning the who, why, and where of his power. Like the citizens of Oz, if you feel comfortable that ImageMagick can help you convert, edit, or compose your images without knowing what goes on behind the curtain, feel free to skip this section. However, if you want to know more about the software and algorithms behind ImageMagick, read on. To fully benefit from this discussion, you should be comfortable with image nomenclature and be familiar with computer programming.</p>
201</div>
202
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]203<h2><a id="overview"></a>Architecture Overview</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]204<div class="doc-section">
205
206<p>An image typically consists of a rectangular region of pixels and metadata. To convert, edit, or compose an image in an efficient manner we need convenient access to any pixel anywhere within the region (and sometimes outside the region). And in the case of an image sequence, we need access to any pixel of any region of any image in the sequence. However, there are hundreds of image formats such JPEG, TIFF, PNG, GIF, etc., that makes it difficult to access pixels on demand. Within these formats we find differences in:</p>
207
208<ul>
209 <li>colorspace (e.g RGB, CMYK, YUV, Lab, etc.)</li>
210 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li>
211 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li>
212 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li>
213 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li>
214 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li>
215</ul>
216
217<p>In addition, some image pixels may require attenuation, some formats permit more than one frame, and some formats contain vector graphics that must first be rasterized (converted from vector to pixels).</p>
218
219<p>An efficient implementation of an image processing algorithm may require we get or set:</p>
220
221<ul>
222 <li>one pixel a time (e.g. pixel at location 10,3)</li>
223 <li>a single scanline (e.g. all pixels from row 4)</li>
224 <li>a few scanlines at once (e.g. pixel rows 4-7)</li>
225 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li>
226 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li>
227 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li>
228 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li>
229 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li>
230 <li>a pixel component that is unsigned or in a floating-point representation (e.g. 0.17836)</li>
231 <li>a high-dynamic range pixel that can include negative values as well as values that exceed the quantum depth (e.g. -0.00716)</li>
232 <li>one or more pixels simultaneously in different threads of execution</li>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]233 <li>all the pixels in memory to take advantage of speed-ups offered by executing in concert across heterogeneous platforms consisting of CPUs, GPUs, and other processors</li>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]234</ul>
235
236<p>In addition, some images include a clip mask that define which pixels are eligible to be updated. Pixels outside the area defined by the clip mask remain untouched.</p>
237
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]238<p>Given the varied image formats and image processing requirements, we implemented the ImageMagick <a href="#cache">pixel cache</a> to provide convenient sequential or parallel access to any pixel on demand anywhere inside the image region (we call these <a href="#authentic-pixels">authentic pixels</a>) and from any image in a sequence. In addition, the pixel cache permits access to pixels outside the boundaries defined by the image (we call these <a href="#virtual-pixels">virtual pixels</a>).</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]239
cristy320dd6e2010-04-16 20:11:40 +0000[diff] [blame]240<p>In addition to pixels, images have a plethora of <a href="#properties">image properties and profiles</a>. Properties include the well known attributes such as width, height, depth, and colorspace. An image may have optional properties which might include the image author, a comment, a create date, and others. Some images also include profiles for color management, or EXIF, IPTC, 8BIM, or XMP informational profiles. ImageMagick provides command line options and programming methods to get, set, or view image properties or profiles or apply profiles.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]241
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]242<p>ImageMagick consists of more than 400,000 lines of C code and optionally depends on several million lines of code in dependent libraries (e.g. JPEG, PNG, TIFF libraries). Given that, one might expect a huge architecture document. However, a great majority of image processing is simply accessing pixels and its metadata and our simple and elegant implementation makes this easy for the ImageMagick developer. We discuss the implementation of the pixel cache and getting and setting image properties and profiles in the next few sections. Next, we discuss using ImageMagick within a <a href="#threads">thread</a> of execution. In the final sections, we discuss <a href="#coders">image coders</a> to read or write a particular image format followed by a few words on creating a <a href="#filters">filter</a> to access or update pixels based on your custom requirements.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]243
244</div>
245
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]246<h2><a id="cache"></a>The Pixel Cache</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]247<div class="doc-section">
248
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]249<p>The ImageMagick pixel cache is a repository for image pixels with up to 5 channels. The first 4 channels are stored contiguously and an optional second area follows with 1 channel. The channels are at the depth specified when ImageMagick was built. The channel depths are 8 bits-per-pixel component for the Q8 version of ImageMagick, 16 bits-per-pixel component for the Q16 version, and 32 bits-per-pixel component for the Q32 version. By default pixel components are unsigned quantities, however, if you use the <a href="../www/high-dynamic-range.html">high dynamic-range</a> version of ImageMagick, the components are 32-bit floating point. The primary 4 channels can hold any value but typically contain red, green, blue, and alpha intensities or cyan, magenta, yellow, and alpha intensities. The optional fifth channel contains the colormap indexes for colormapped images or the black channel for CMYK images. The pixel cache storage may be heap memory, anonymous memory mapped memory, disk-backed memory mapped, or on disk. The pixel cache is reference-counted. Only the cache properties are copied when the cache is cloned. The cache pixels are subsequently copied only when you signal your intention to update any of the pixels.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]250
251<h3>Create the Pixel Cache</h3>
252<div class="doc-section">
253
254<p>The pixel cache is associated with an image when it is created and it is initialized when you try to get or put pixels. Here are three common methods to associate a pixel cache with an image:</p>
255
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]256<dl>
257<dt>Create an image canvas initialized to the background color:</dt>
258<dd><p class="code">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]259 image=AllocateImage(image_info);
260 if (SetImageExtent(image,640,480) == MagickFalse)
261 { /* an exception was thrown */ }
262 (void) QueryMagickColor("red",&amp;image-&gt;background_color,&amp;image-&gt;exception);
263 SetImageBackgroundColor(image);
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]264</p></dd>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]265
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]266<dt>Create an image from a JPEG image on disk:</dt>
267<dd><p class="code">
268 (void) strcpy(image_info-&gt;filename,"image.jpg"):
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]269 image=ReadImage(image_info,exception);
270 if (image == (Image *) NULL)
271 { /* an exception was thrown */ }
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]272</p></dd>
273<dt>Create an image from a memory based image:</dt>
274<dd><p class="code">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]275 image=BlobToImage(blob_info,blob,extent,exception);
276 if (image == (Image *) NULL)
277 { /* an exception was thrown */ }
cristyec6b4752011-01-08 03:16:23 +0000[diff] [blame]278</p></dd>
279</dl>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]280
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]281<p>In our discussion of the pixel cache, we use the <a href="../www/magick-core.html">MagickCore API</a> to illustrate our points, however, the principles are the same for other program interfaces to ImageMagick.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]282
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]283<p>When the pixel cache is initialized, pixels are scaled from whatever bit depth they originated from to that required by the pixel cache. For example, a 1-channel 1-bit monochrome PBM image is scaled to a 4 channel 8-bit RGBA image, if you are using the Q8 version of ImageMagick, and 16-bit RGBA for the Q16 version. You can determine which version you have with the <a href="../www/command-line-options.html#version">&#x2011;version</a> option: </p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]284
cristy2d67ddd2011-02-13 15:38:23 +0000[diff] [blame]285<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 6.6.7-7 2010-71-71 Q16 http://www.imagemagick.org</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]286<p>As you can see, the convenience of the pixel cache sometimes comes with a trade-off in storage (e.g. storing a 1-bit monochrome image as 16-bit RGBA is wasteful) and speed (i.e. storing the entire image in memory is generally slower than accessing one scanline of pixels at a time). In most cases, the benefits of the pixel cache typically outweigh any disadvantages.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]287</div>
288
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]289<h3><a id="authentic-pixels"></a>Access the Pixel Cache</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]290<div class="doc-section">
291
292<p>Once the pixel cache is associated with an image, you typically want to get, update, or put pixels into it. We refer to pixels inside the image region as <em>authentic pixels</em> and outside the region as <em>virtual pixels</em>. Use these methods to access the pixels in the cache:</p>
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]293<ul>
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]294 <li><a href="../www/api/cache.html#GetVirtualPixels">GetVirtualPixels()</a> gets pixels that you do not intend to modify or pixels that lie outside the image region (e.g. pixel @ -1,-3)</li>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]295 <li><a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> gets pixels that you intend to modify</li>
296 <li><a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> queue pixels that you intend to modify</li>
297 <li><a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> update the pixel cache with any modified pixels</li>
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]298</ul>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]299
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]300<p>Here is a typical <a href="../www/magick-core.html">MagickCore</a> code snippet for manipulating pixels in the pixel cache. In our example, we copy pixels from the input image to the output image and decrease the intensity by 10%:</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]301
302<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]303 const PixelPacket
304 *p;
305
306 PixelPacket
307 *q;
308
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]309 ssize_t
310 x,
311 y;
312
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]313 destination=CloneImage(source,source->columns,source->rows,MagickTrue,
314 exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]315 if (destination == (Image *) NULL)
316 { /* an exception was thrown */ }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]317 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]318 {
319 p=GetVirtualPixels(source,0,y,source-&gt;columns,1,exception);
320 q=GetAuthenticPixels(destination,0,y,destination-&gt;columns,1,exception);
321 if ((p == (const PixelPacket *) NULL) || (q == (PixelPacket *) NULL)
322 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]323 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]324 {
325 q-&gt;red=90*p-&gt;red/100;
326 q-&gt;green=90*p-&gt;green/100;
327 q-&gt;blue=90*p-&gt;blue/100;
328 q-&gt;opacity=90*p-&gt;opacity/100;
329 p++;
330 q++;
331 }
332 if (SyncAuthenticPixels(destination,exception) == MagickFalse)
333 break;
334 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]335 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]336 { /* an exception was thrown */ }
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]337</div>
338
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]339<p>When we first create the destination image by cloning the source image, the pixel cache pixels are not copied. They are only copied when you signal your intentions to modify the pixel cache by calling <a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> or <a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a>. Use <a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> if you want to set new pixel values rather than update existing ones. You could use GetAuthenticPixels() to set pixel values but it is slightly more efficient to use QueueAuthenticPixels() instead. Finally, use <a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> to ensure any updated pixels are pushed to the pixel cache.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]340
341<p>Recall how we mentioned that the indexes of a colormapped image or the black channel of a CMYK image are stored separately. Use <a href="../www/api/cache.html#GetVirtualIndexes">GetVirtualIndexes()</a> (to read the indexes) or <a href="../www/api/cache.html#GetAuthenticIndexes">GetAuthenticIndexes()</a> (to update the indexes) to gain access to this channel. For example, to print the colormap indexes, use:</p>
342
343<pre class="code">
344 const IndexPacket
345 *indexes;
346
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]347 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]348 {
349 p=GetVirtualPixels(source,0,y,source-&gt;columns,1);
350 if (p == (const PixelPacket *) NULL)
351 break;
352 indexes=GetVirtualIndexes(source);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]353 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]354 (void) printf("%d\n",indexes[x];
355 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]356 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]357 /* an exception was thrown */
358</pre>
359
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]360<p>The pixel cache manager decides whether to give you direct or indirect access to the image pixels. In some cases the pixels are staged to an intermediate buffer-- and that is why you must call SyncAuthenticPixels() to ensure this buffer is <em>pushed</em> out to the pixel cache to guarantee the corresponding pixels in the cache are updated. For this reason we recommend that you only read or update a scanline or a few scanlines of pixels at a time. However, you can get any rectangular region of pixels you want. GetAuthenticPixels() requires that the region you request is within the bounds of the image area. For a 640 by 480 image, you can get a scanline of 640 pixels at row 479 but if you ask for a scanline at row 480, an exception is returned (rows are numbered starting at 0). GetVirtualPixels() does not have this constraint. For example,</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]361
362<pre class="code">
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]363 p=GetVirtualPixels(source,-3,-3,source-&gt;columns+3,6,exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]364</pre>
365
366<p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p>
367</div>
368
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]369<h3><a id="virtual-pixels"></a>Virtual Pixels</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]370<div class="doc-section">
371
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]372<p>There are a plethora of image processing algorithms that require a neighborhood of pixels about a pixel of interest. The algorithm typically includes a caveat concerning how to handle pixels around the image boundaries, known as edge pixels. With virtual pixels, you do not need to concern yourself about special edge processing other than choosing which virtual pixel method is most appropriate for your algorithm.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]373 <p>Access to the virtual pixels are controlled by the <a href="../www/api/cache.html#SetImageVirtualPixelMethod">SetImageVirtualPixelMethod()</a> method from the MagickCore API or the <a href="../www/command-line-options.html#virtual-pixel">&#x2011;virtual&#x2011;pixel</a> option from the command line. The methods include:</p>
374
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]375<pre class="text" style="font-size: 90%;">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]376 background: the area surrounding the image is the background color
377 black: the area surrounding the image is black
378 checker-tile: alternate squares with image and background color
379 dither: non-random 32x32 dithered pattern
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]380 edge: extend the edge pixel toward infinity (default)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]381 gray: the area surrounding the image is gray
382 horizontal-tile: horizontally tile the image, background color above/below
383 horizontal-tile-edge: horizontally tile the image and replicate the side edge pixels
384 mirror: mirror tile the image
385 random: choose a random pixel from the image
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]386 tile: tile the image
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]387 transparent: the area surrounding the image is transparent blackness
388 vertical-tile: vertically tile the image, sides are background color
389 vertical-tile-edge: vertically tile the image and replicate the side edge pixels
390 white: the area surrounding the image is white
391</pre>
392
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]393</div>
394
395<h3>Cache Storage and Resource Requirements</h3>
396<div class="doc-section">
397
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]398<p>Recall that this simple and elegant design of the ImageMagick pixel cache comes at a cost in terms of storage and processing speed. The pixel cache storage requirements scales with the area of the image and the bit depth of the pixel components. For example, if we have a 640 by 480 image and we are using the Q16 version of ImageMagick, the pixel cache consumes image <em>width * height * bit-depth / 8 * channels</em> bytes or approximately 2.3 mebibytes (i.e. 640 * 480 * 2 * 4). Not too bad, but what if your image is 25000 by 25000 pixels? The pixel cache requires approximately 4.7 gibibytes of storage. Ouch. ImageMagick accounts for possible huge storage requirements by caching large images to disk rather than memory. Typically the pixel cache is stored in memory using heap memory. If heap memory is exhausted, pixels are stored in in an anonymous map; if the anonymous memory map is exhausted, we create the pixel cache on disk and attempt to memory-map it; and if memory-map memory is exhausted, we simply use standard disk I/O. Disk storage is cheap but it is also very slow, upwards of 1000 times slower than memory. We can get some speed improvements, up to 5 times, if we use memory mapping to the disk-based cache. These decisions about storage are made <em>automagically</em> by the pixel cache manager negotiating with the operating system. However, you can influence how the pixel cache manager allocates the pixel cache with <em>cache resource limits</em>. The limits include:</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]399
400<dl class="doc">
401 <dt class="doc">files</dt>
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]402 <dd>maximum number of open pixel cache files. When this limit is exceeded, any subsequent pixels cached to disk are closed and reopened on demand. This behavior permits a large number of images to be accessed simultaneously on disk, but without a speed penalty due to repeated open/close calls.</dd>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]403 <dt class="doc">area</dt>
404 <dd>maximum area in bytes of any one image that can reside in the pixel cache memory. If this limit is exceeded, the image is automagically cached to disk.</dd>
405 <dt class="doc">memory</dt>
406 <dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd>
407 <dt class="doc">map</dt>
408 <dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd>
409 <dt class="doc">disk</dt>
410 <dd>maximum amount of disk space in bytes permitted for use by the pixel cache. If this limit is exceeded, the pixel cache is not created and a fatal exception is thrown.</dd>
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]411 <dt class="doc">thread</dt>
412 <dd>maximum number of threads that are permitted to run in parallel.</dd>
413 <dt class="doc">time</dt>
414 <dd>maximum number of seconds that the process is permitted to execute. When this limit is exceeded, an exception is thrown and processing stops.</dd>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]415</dl>
416
417<p>To determine the current setting of these limits, use this command:</p>
418
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]419<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -list resource</span></p><pre class="text">
420File Area Memory Map Disk Thread Time
cristy2c839602010-04-03 02:32:08 +0000[diff] [blame]421-------------------------------------------------------------------------------
cristy5c4585b2010-11-11 00:13:57 +0000[diff] [blame]422 768 1.0386GB 3.8692GiB 7.7384GiB unlimited 4 unlimited
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]423</pre>
424
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]425<p>You can set these limits either as a <a href="../www/resources.html#configure">policy</a> (see <a href="../www/source/policy.xml">policy.xml</a>), with an <a href="../www/resources.html#environment">environment variable</a>, with the <a href="../www/command-line-options.html#limit">-limit</a> command line option, or with the <a href="../www/api/resource.html#SetMagickResourceLimit">SetMagickResourceLimit()</a> MagickCore API method. As an example, our online web interface to ImageMagick, <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">ImageMagick Studio</a>, has an area limit of 64 megabytes, a memory limit of 128 mebibytes and a map limit of 256 mebibytes and a disk limit of 1 gigabytes. Since we process multiple simultaneous sessions, we don't want any one session consuming all the available memory. Instead large images are cached to disk. If the image is too large and exceeds the pixel cache disk limit, the program exits. In addition, we place a 60 second time limit to prevent any run-away processing tasks.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]426
427<p>Note, the cache limits are global, meaning if you create several images, the combined resource requirements are compared to the limit to determine the pixel cache storage disposition.</p>
428</div>
429
430<h3>Cache Views</h3>
431<div class="doc-section">
432
433<p>GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels(), and SyncAuthenticPixels() from the MagickCore API can only deal with one pixel cache area per image at a time. Suppose you want to access the first and last scanline from the same image at the same time? The solution is to use a <em>cache view</em>. A cache view permits you to access as many areas simultaneously in the pixel cache as you require. The cache view <a href="../www/api/cache-view.html">methods</a> behave like the previous methods except you must first open a view and close it when you are finished with it. Here is a snippet of MagickCore code that permits us to access two areas of an image simultaneously:</p>
434
435<pre class="code">
436 CacheView
437 *view_1,
438 *view_2;
439
440 view_1=OpenCacheView(source);
441 view_2=OpenCacheView(source);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]442 for (y=0; y &lt; (ssize_t) source-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]443 {
444 u=GetCacheViewVirtualPixels(view_1,0,y,source-&gt;columns,1,exception);
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]445 v=GetCacheViewVirtualPixels(view_2,0,source-&gt;rows-y-1,source-&gt;columns,1,
446 exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]447 if ((u == (const PixelPacket *) NULL) || (v == (const PixelPacket *) NULL))
448 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]449 for (x=0; x &lt; (ssize_t) source-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]450 {
451 /* do something with u &amp; v here */
452 }
453 }
454 view_1=CloseCacheView(view_1);
455 view_2=CloseCacheView(view_2);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]456 if (y &lt; (ssize_t) source-&gt;rows)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]457 { /* an exception was thrown */ }
458</pre>
459</div>
460
461<h3>Magick Persistent Cache Format</h3>
462<div class="doc-section">
463
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]464<p>Recall that each image format is decoded by ImageMagick and the pixels are deposited in the pixel cache. If you write an image, the pixels are read from the pixel cache and encoded as required by the format you are writing (e.g. GIF, PNG, etc.). The Magick Persistent Cache (MPC) format is designed to eliminate the overhead of decoding and encoding pixels to and from an image format. MPC writes two files. One, with the extension <kbd>.mpc</kbd>, retains all the properties associated with the image or image sequence (e.g. width, height, colorspace, etc.) and the second, with the extension <kbd>.cache</kbd>, is the pixel cache in the native raw format. When reading an MPC image file, ImageMagick reads the image properties and memory maps the pixel cache on disk eliminating the need for decoding the image pixels. The tradeoff is in disk space. MPC is generally larger in file size than most other image formats.</p>
cristy5063d812010-10-19 16:28:10 +0000[diff] [blame]465<p>The most efficient use of MPC image files is a write-once, read-many-times pattern. For example, your workflow requires extracting random blocks of pixels from the source image. Rather than re-reading and possibly decompressing the source image each time, we use MPC and map the image directly to memory.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]466</div>
467
468<h3>Best Practices</h3>
469<div class="doc-section">
470
471<p>Although you can request any pixel from the pixel cache, any block of pixels, any scanline, multiple scanlines, any row, or multiple rows with the GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels, GetCacheViewVirtualPixels(), GetCacheViewAuthenticPixels(), and QueueCacheViewAuthenticPixels() methods, ImageMagick is optimized to return a few pixels or a few pixels rows at time. There are additional optimizations if you request a single scanline or a few scanlines at a time. These methods also permit random access to the pixel cache, however, ImageMagick is optimized for sequential access.</p>
472
473<p>If you update pixels returned from GetAuthenticPixels() or GetCacheViewAuthenticPixels(), don't forget to call SyncAuthenticPixels() or SyncCacheViewAuthenticPixels() respectively to ensure your changes are synchronized with the pixel cache.</p>
474
475<p>Use QueueAuthenticPixels() or QueueCacheViewAuthenticPixels() if you are setting an initial pixel value. The GetAuthenticPixels() or GetCacheViewAuthenticPixels() method reads pixels from the cache and if you are setting an initial pixel value, this read is unnecessary. Don't forget to call SyncAuthenticPixels() or SyncCacheViewAuthenticPixels() respectively to push your updates to the pixel cache.</p>
476
477<p>GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels(), and SyncAuthenticPixels() are slightly more efficient than their cache view counter-parts. However, cache views are required if you need access to more than one region of the image simultaneously or if more than one <a href="#threads">thread of execution</a> is accessing the image.</p>
478
479<p>You can request pixels outside the bounds of the image with GetVirtualPixels() or GetCacheViewVirtualPixels(), however, it is more efficient to request pixels within the confines of the image region.</p>
480
481<p>Although you can force the pixel cache to disk using appropriate resource limits, disk access can be upwards of 1000 times slower than memory access. For fast, efficient, access to the pixel cache, try to keep the pixel cache in heap memory or anonymous mapped memory.</p>
482
483<p>The ImageMagick Q16 version of ImageMagick permits you to read and write 16 bit images without scaling but the pixel cache consumes twice as much resources as the Q8 version. If your system has constrained memory or disk resources, consider the Q8 version of ImageMagick. In addition, the Q8 version typically executes faster than the Q16 version.</p>
484
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]485<p>A great majority of image formats and algorithms restrict themselves to a fixed range of pixel values from 0 to some maximum value, for example, the Q16 version of ImageMagick permit intensities from 0 to 65535. High dynamic-range imaging (HDRI), however, permits a far greater dynamic range of exposures (i.e. a large difference between light and dark areas) than standard digital imaging techniques. HDRI accurately represents the wide range of intensity levels found in real scenes ranging from the brightest direct sunlight to the deepest darkest shadows. Enable <a href="../www/high-dynamic-range.html">HDRI</a> at ImageMagick build time to deal with high dynamic-range images, but be mindful that each pixel component is a 32-bit floating point value. In addition, pixel values are not clamped by default so some algorithms may perform differently than the non-HDRI version.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]486
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]487<p>If you are dealing with large images, make sure the pixel cache is written to a disk area with plenty of free space. Under Unix, this is typically <kbd>/tmp</kbd> and for Windows, <kbd>c:/temp</kbd>. You can tell ImageMagick to write the pixel cache to an alternate location with the MAGICK_TEMPORARY_PATH environment variable. For example,</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]488
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]489<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>export MAGICK_TEMPORARY_PATH=/data/magick</span></p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]490
491<p>If you plan on processing the same image many times, consider the MPC format. Reading a MPC image has near-zero overhead because its in the native pixel cache format eliminating the need for decoding the image pixels. Here is an example:</p>
492
493<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.tif image.mpc</span><span class='crtout'></span><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.mpc -crop 100x100+0+0 +repage 1.png</span><span class='crtout'></span><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.mpc -crop 100x100+100+0 +repage 2.png</span><span class='crtout'></span><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.mpc -crop 100x100+200+0 +repage 3.png</span></p>
494<p>MPC is ideal for web sites. It reduces the overhead of reading and writing an image. We use it exclusively at our <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">online image studio</a>.</p>
495</div>
496
497</div>
498
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]499<h2><a id="stream"></a>Streaming Pixels</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]500<div class="doc-section">
501
502<p>ImageMagick provides for streaming pixels as they are read from or written to an image. This has several advantages over the pixel cache. The time and resources consumed by the pixel cache scale with the area of an image, whereas the pixel stream resources scale with the width of an image. The disadvantage is the pixels must be consumed as they are streamed so there is no persistence.</p>
503
504<p>Use <a href="../www/api/stream.html#ReadStream">ReadStream()</a> or <a href="../www/api/stream.html#WriteStream">WriteStream()</a> with an appropriate callback method in your MagickCore program to consume the pixels as they are streaming. Here's an abbreviated example of using ReadStream:</p>
505
506<pre class="code">
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]507static size_t StreamPixels(const Image *image,const void *pixels,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]508 const size_t columns)
509{
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]510 register const PixelPacket
511 *p;
512
513 MyData
514 *my_data;
515
516 my_data=(MyData *) image->client_data;
517 p=(PixelPacket *) pixels;
518 if (p != (const PixelPacket *) NULL)
519 {
520 /* process pixels here */
521 }
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]522 return(columns);
523}
524
525...
526/* invoke the pixel stream here */
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]527image_info->client_data=(void *) MyData;
528image=ReadStream(image_info,&amp;StreamPixels,exception);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]529</pre>
530
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]531<p>We also provide a lightweight tool, <a href="../www/stream.html">stream</a>, to stream one or more pixel components of the image or portion of the image to your choice of storage formats. It writes the pixel components as they are read from the input image a row at a time making <a href="../www/stream.html">stream</a> desirable when working with large images or when you require raw pixel components. A majority of the image formats stream pixels (red, green, and blue) from left to right and top to bottom. However, a few formats do not support this common ordering (e.g. the PSD format).</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]532
533</div>
534
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]535<h2><a id="properties"></a>Image Properties and Profiles</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]536<div class="doc-section">
537
538<p>Images have metadata associated with them in the form of properties (e.g. width, height, description, etc.) and profiles (e.g. EXIF, IPTC, color management). ImageMagick provides convenient methods to get, set, or update image properties and get, set, update, or apply profiles. Some of the more popular image properties are associated with the Image structure in the MagickCore API. For example:</p>
539
540<pre class="code">
541 (void) printf("image width: %lu, height: %lu\n",image-&gt;columns,image-&gt;rows);
542</pre>
543
544<p>For a great majority of image properties, such as an image comment or description, we use the <a href="../www/api/property.html#GetImageProperty">GetImageProperty()</a> and <a href="../www/api/property.html#SetImageProperty">SetImageProperty()</a> methods. Here we set a property and fetch it right back:</p>
545
546<pre class="code">
547 const char
548 *comment;
549
550 (void) SetImageProperty(image,"comment","This space for rent");
551 comment=GetImageProperty(image,"comment");
552 if (comment == (const char *) NULL)
553 (void) printf("Image comment: %s\n",comment);
554</pre>
555
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]556<p>ImageMagick supports artifacts with the GetImageArtifact() and SetImageArtifact() methods. Artifacts are stealth properties that are not exported to image formats (e.g. PNG).</p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]557
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]558<p>Image profiles are handled with <a href="../www/api/profile.html#GetImageProfile">GetImageProfile()</a>, <a href="../www/api/profile.html#SetImageProfile">SetImageProfile()</a>, and <a href="../www/api/profile.html#ProfileImage">ProfileImage()</a> methods. Here we set a profile and fetch it right back:</p>
559
560<pre class="code">
561 StringInfo
562 *profile;
563
564 profile=AcquireStringInfo(length);
565 SetStringInfoDatum(profile,my_exif_profile);
566 (void) SetImageProfile(image,"EXIF",profile);
567 DestroyStringInfo(profile);
568 profile=GetImageProfile(image,"EXIF");
569 if (profile != (StringInfo *) NULL)
570 (void) PrintStringInfo(stdout,"EXIF",profile);
571</pre>
572
573</div>
574
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]575<h2><a id="tera-pixel"></a>Large Image Support</h2>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]576<div class="doc-section">
cristy94fb0312010-06-09 16:06:13 +0000[diff] [blame]577<p>ImageMagick can read, process, or write mega-, giga-, or tera-pixel image sizes. An image width or height can range from 1 to 2 giga-pixels on a 32 bit OS and up to 9 exa-pixels on a 64-bit OS. Note, that some image formats have restrictions on image size. For example, Photoshop images are limited to 300,000 pixels for width or height. Here we resize an image to a quarter million pixels square:</p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]578
579<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert logo: -resize 250000x250000 logo.miff</span></p>
cristyc3186d52010-06-04 13:55:23 +0000[diff] [blame]580<p>For large images, ImageMagick will likely create a pixel cache on disk. Make sure you have plenty of temporary disk space. If your default temporary disk partition is too small, tell ImageMagick to use another partition with plenty of free space. For example:</p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]581
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]582<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -define registry:temporary-path=/data/tmp logo: \ <br/> -resize 250000x250000 logo.miff</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]583<p>To ensure large images do not consume all the memory on your system, force the image pixels to memory-mapped disk with resource limits:</p>
584
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]585<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -define registry:temporary-path=/data/tmp -limit memory 16mb \ <br/> logo: -resize 250000x250000 logo.miff</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]586<p>Here we force all image pixels to disk:</p>
587
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]588<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -define registry:temporary-path=/data/tmp -limit area 0 \ <br/> logo: -resize 250000x250000 logo.miff</span></p>
cristybac7a162010-06-15 19:57:29 +0000[diff] [blame]589<p>Caching pixels to disk is about 1000 times slower than memory. Expect long run times when processing large images on disk with ImageMagick. You can monitor progress with this command:</p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]590
cristyfe0019b2010-06-07 02:23:32 +0000[diff] [blame]591<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -monitor -define registry:temporary-path=/data/tmp -limit area 0 \ <br/> logo: -resize 250000x250000 logo.miff</span></p></div>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]592
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]593<h2><a id="threads"></a>Threads of Execution</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]594<div class="doc-section">
595
cristy5c4585b2010-11-11 00:13:57 +0000[diff] [blame]596<p>Many of ImageMagick's internal algorithms are threaded to take advantage of speed-ups offered by the multicore processor chips. However, you are welcome to use ImageMagick algorithms in your threads of execution with the exception of the MagickCore's GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels(), or SyncAuthenticPixels() pixel cache methods. These methods are intended for one thread of execution only with the exception of an OpenMP parallel section. To access the pixel cache with more than one thread of execution, use a cache view. We do this for the <a href="../www/api/composite.html#CompositeImage">CompositeImage()</a> method, for example. Suppose we want to composite a single image over a different image in each thread of execution. If we use GetVirtualPixels(), the results are unpredictable because multiple threads would likely be asking for different areas of the pixel cache simultaneously. Instead we use GetCacheViewVirtualPixels() which creates a unique view for each thread of execution ensuring our program behaves properly regardless of how many threads are invoked. The other program interfaces, such as the <a href="../www/magick-wand.html">MagickWand API</a>, are completely thread safe so there are no special precautions for threads of execution.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]597
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]598<p>Here is an MagickCore code snippet that takes advantage of threads of execution with the <a href="http://en.wikipedia.org/wiki/OpenMP">OpenMP</a> programming paradigm:</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]599
600<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]601{
602 CacheView
603 *image_view;
604
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]605 MagickBooleanType
606 status;
607
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]608 ssize_t
609 y;
610
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]611 status=MagickTrue;
612 image_view=AcquireCacheView(image);
613 #pragma omp parallel for schedule(dynamic,4) shared(status)
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]614 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]615 {
616 register IndexPacket
617 *indexes;
618
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]619 register PixelPacket
620 *q;
621
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]622 register ssize_t
623 x;
624
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]625 if (status == MagickFalse)
626 continue;
627 q=GetCacheViewAuthenticPixels(image_view,0,y,image-&gt;columns,1,exception);
628 if (q == (PixelPacket *) NULL)
629 {
630 status=MagickFalse;
631 continue;
632 }
633 indexes=GetCacheViewAuthenticIndexQueue(image_view);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]634 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]635 {
636 q-&gt;red= ...
637 q-&gt;green= ...
638 q-&gt;blue= ...
639 q-&gt;opacity= ...
640 if (indexes != (IndexPacket *) NULL)
641 indexes[x]= ...
642 q++;
643 }
644 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse)
645 status=MagickFalse;
646 }
647 image_view=DestroyCacheView(image_view);
648 if (status == MagickFalse)
649 perror("something went wrong");
650}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]651</div>
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]652<p>This code snippet converts an uncompressed Windows bitmap to a Magick++ image:</p>
653<div class="viewport">
654#include "Magick++.h"
655#include &lt;assert.h&gt;
656#include "omp.h"
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]657
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]658void ConvertBMPToImage(const BITMAPINFOHEADER *bmp_info,
659 const unsigned char *restrict pixels,Magick::Image *image)
660{
661 /*
662 Prepare the image so that we can modify the pixels directly.
663 */
664 assert(bmp_info->biCompression == BI_RGB);
665 assert(bmp_info->biWidth == image->columns());
666 assert(abs(bmp_info->biHeight) == image->rows());
667 image->modifyImage();
668 if (bmp_info->biBitCount == 24)
669 image->type(MagickCore::TrueColorType);
670 else
671 image->type(MagickCore::TrueColorMatteType);
672 register unsigned int bytes_per_row=bmp_info->biWidth*bmp_info->biBitCount/8;
673 if (bytes_per_row % 4 != 0) {
674 bytes_per_row=bytes_per_row+(4-bytes_per_row % 4); // divisible by 4.
675 }
676 /*
677 Copy all pixel data, row by row.
678 */
679 #pragma omp parallel for
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]680 for (int y=0; y &lt; int(image->rows()); y++)
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]681 {
682 int row=(bmp_info->biHeight > 0) ? (image->rows()-y-1) : y;
683 register const unsigned char *restrict p=pixels+row*bytes_per_row;
684 register MagickCore::PixelPacket *restrict q=
685 image->setPixels(0,y,image->columns(),1);
cristy2bd2a982011-02-15 00:52:58 +0000[diff] [blame]686 for (int x=0; x &lt; int(image->columns()); x++)
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]687 {
688 q->blue=p[0];
689 q->green=p[1];
690 q->red=p[2];
691 if (bmp_info->biBitCount == 32) {
692 q->opacity=p[3];
693 }
694 q++;
695 p+=bmp_info->biBitCount/8;
696 }
697 image->syncPixels(); // sync pixels to pixel cache.
698 }
699 return;
700}
701</div>
cristyfbb4a972010-06-30 17:42:22 +0000[diff] [blame]702
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]703<p>If you call the ImageMagick API from your OpenMP-enabled application and you intend to dynamically increase the number of threads available in subsequent parallel regions, be sure to perform the increase <em>before</em> you call the API otherwise ImageMagick may fault.</p>
704
cristy8030a5b2010-09-17 18:31:49 +0000[diff] [blame]705<p><a href="../www/api/wand-view.html">MagickWand</a> supports wand views. A view iterates over the entire, or portion, of the image in parallel and for each row of pixels, it invokes a callback method you provide. This limits most of your parallel programming activity to just that one module. There are similar methods in <a href="../www/api/image-view.html">MagickCore</a>. For an example, see the same sigmoidal contrast algorithm implemented in both <a href="../www/magick-wand.html#wand-view">MagickWand</a> and <a href="../www/magick-core.html#image-view">MagickCore</a>.</p>
cristyfe7ce342010-06-22 15:41:50 +0000[diff] [blame]706
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]707<p>In most circumstances, the default number of threads is set to the number of processor cores on your system for optimal performance. However, if your system is hyperthreaded or if you are running on a virtual host and only a subset of the processors are available to your server instance, you might get an increase in performance by setting the thread <a href="../www/resources.html#configure">policy</a> or the <a href="../www/resources.html#environment">MAGICK_THREAD_LIMIT</a> environment variable. For example, your virtual host has 8 processors but only 2 are assigned to your server instance. The default of 8 threads can cause severe performance problems. One solution is to limit the number of threads to the available processors in your <a href="../www/source/policy.xml">policy.xml</a> configuration file:</p>
cristyce66ab12010-10-21 23:36:32 +0000[diff] [blame]708
709<pre class="text">
710 &lt;policy domain="resource" name="thread" value="2"/>
711</pre>
712
713<p>Or suppose your 12 core hyperthreaded computer defaults to 24 threads. Set the MAGICK_THREAD_LIMIT environment variable and you will likely get improved performance:</p>
714
715<pre class="text">
716 export MAGICK_THREAD_LIMIT=12
717</pre>
718
719<p>The OpenMP committee has not defined the behavior of mixing OpenMP with other threading models such as Posix threads. However, using modern releases of Linux, OpenMP and Posix threads appear to interoperate without complaint. If you want to use Posix threads from a program module that calls one of the ImageMagick application programming interfaces (e.g. MagickCore, MagickWand, Magick++, etc.) from Mac OS X or an older Linux release, you may need to disable OpenMP support within ImageMagick. Add the <kbd>--disable-openmp</kbd> option to the configure script command line and rebuild and reinstall ImageMagick.</p>
720
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]721</div>
722
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]723<h2><a id="distributed"></a>Heterogeneous Distributed Processing</h2>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]724<div class="doc-section">
725<p>ImageMagick includes support for heterogeneous distributed processing with the <a href="http://en.wikipedia.org/wiki/OpenCL">OpenCL</a> framework. OpenCL kernels within ImageMagick permit image processing algorithms to execute across heterogeneous platforms consisting of CPUs, GPUs, and other processors. Depending on your platform, speed-ups can be an order of magnitude faster than the traditional single CPU.</p>
726
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]727<p>First verify that your version of ImageMagick includes support for the OpenCL feature:</p>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]728
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]729<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Features: OpenMP OpenCL</span></p>
730<p>If so, run this command to realize a significant speed-up for image convolution:</p>
731
cristy4949d522010-03-12 18:41:34 +0000[diff] [blame]732<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.png convolve '-1, -1, -1, -1, 9, -1, -1, -1, -1' \ <br/> convolve.png</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]733<p>If an accelerator is not available or if the accelerator fails to respond, ImageMagick reverts to the non-accelerated convolution algorithm.</p>
734
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]735<p>Here is an example OpenCL kernel that convolves an image:</p>
736
737<div class="viewport">
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]738static inline long ClampToCanvas(const long offset,const ulong range)
739{
740 if (offset &lt; 0L)
741 return(0L);
742 if (offset >= range)
743 return((long) (range-1L));
744 return(offset);
745}
746
747static inline CLQuantum ClampToQuantum(const double value)
748{
749 if (value &lt; 0.0)
750 return((CLQuantum) 0);
751 if (value >= (double) QuantumRange)
752 return((CLQuantum) QuantumRange);
753 return((CLQuantum) (value+0.5));
754}
755
756__kernel void Convolve(const __global CLPixelType *source,__constant double *filter,
757 const ulong width,const ulong height,__global CLPixelType *destination)
758{
759 const ulong columns = get_global_size(0);
760 const ulong rows = get_global_size(1);
761
762 const long x = get_global_id(0);
763 const long y = get_global_id(1);
764
765 const double scale = (1.0/QuantumRange);
766 const long mid_width = (width-1)/2;
767 const long mid_height = (height-1)/2;
768 double4 sum = { 0.0, 0.0, 0.0, 0.0 };
769 double gamma = 0.0;
770 register ulong i = 0;
771
772 for (long v=(-mid_height); v &lt;= mid_height; v++)
773 {
774 for (long u=(-mid_width); u &lt;= mid_width; u++)
775 {
cristy4103d562010-12-10 01:38:54 +0000[diff] [blame]776 register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u,
777 columns);
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]778 const double alpha=scale*(QuantumRange-source[index].w);
779 sum.x+=alpha*filter[i]*source[index].x;
780 sum.y+=alpha*filter[i]*source[index].y;
781 sum.z+=alpha*filter[i]*source[index].z;
782 sum.w+=filter[i]*source[index].w;
783 gamma+=alpha*filter[i];
784 i++;
785 }
786 }
787
788 gamma=1.0/(fabs(gamma) &lt;= MagickEpsilon ? 1.0 : gamma);
789 const ulong index=y*columns+x;
790 destination[index].x=ClampToQuantum(gamma*sum.x);
791 destination[index].y=ClampToQuantum(gamma*sum.y);
792 destination[index].z=ClampToQuantum(gamma*sum.z);
793 destination[index].w=ClampToQuantum(sum.w);
794};
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]795</div>
796
cristy37f02952010-03-24 19:47:41 +0000[diff] [blame]797<p>See <a href="http://trac.imagemagick.org/browser/ImageMagick/trunk/magick/accelerate.c">magick/accelerate.c</a> for a complete implementation of image convolution with an OpenCL kernel.</p>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]798
799</div>
800
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]801<h2><a id="coders"></a>Custom Image Coders</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]802<div class="doc-section">
803
804<p>An image coder (i.e. encoder / decoder) is responsible for registering, optionally classifying, optionally reading, optionally writing, and unregistering one image format (e.g. PNG, GIF, JPEG, etc.). Registering an image coder alerts ImageMagick a particular format is available to read or write. While unregistering tells ImageMagick the format is no longer available. The classifying method looks at the first few bytes of an image and determines if the image is in the expected format. The reader sets the image size, colorspace, and other properties and loads the pixel cache with the pixels. The reader returns a single image or an image sequence (if the format supports multiple images per file), or if an error occurs, an exception and a null image. The writer does the reverse. It takes the image properties and unloads the pixel cache and writes them as required by the image format.</p>
805
806<p>Here is a listing of a sample <a href="../www/source/mgk.c">custom coder</a>. It reads and writes images in the MGK image format which is simply an ID followed by the image width and height followed by the RGB pixel values.</p>
807
808<div class="viewport">
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]809/*
810 Include declarations.
811*/
812#include "magick/studio.h"
813#include "magick/blob.h"
814#include "magick/blob-private.h"
815#include "magick/colorspace.h"
816#include "magick/exception.h"
817#include "magick/exception-private.h"
818#include "magick/image.h"
819#include "magick/image-private.h"
820#include "magick/list.h"
821#include "magick/magick.h"
822#include "magick/memory_.h"
823#include "magick/monitor.h"
824#include "magick/monitor-private.h"
825#include "magick/quantum-private.h"
826#include "magick/static.h"
827#include "magick/string_.h"
828#include "magick/module.h"
829
830/*
831 Forward declarations.
832*/
833static MagickBooleanType
834 WriteMGKImage(const ImageInfo *,Image *);
835
836/*
837%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
838% %
839% %
840% %
841% I s M G K %
842% %
843% %
844% %
845%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
846%
847% IsMGK() returns MagickTrue if the image format type, identified by the
848% magick string, is MGK.
849%
850% The format of the IsMGK method is:
851%
852% MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
853%
854% A description of each parameter follows:
855%
856% o magick: This string is generally the first few bytes of an image file
857% or blob.
858%
859% o length: Specifies the length of the magick string.
860%
861*/
862static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
863{
864 if (length &lt; 7)
865 return(MagickFalse);
866 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0)
867 return(MagickTrue);
868 return(MagickFalse);
869}
870
871/*
872%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
873% %
874% %
875% %
876% R e a d M G K I m a g e %
877% %
878% %
879% %
880%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
881%
882% ReadMGKImage() reads a MGK image file and returns it. It allocates
883% the memory necessary for the new Image structure and returns a pointer to
884% the new image.
885%
886% The format of the ReadMGKImage method is:
887%
888% Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception)
889%
890% A description of each parameter follows:
891%
892% o image_info: the image info.
893%
894% o exception: return any errors or warnings in this structure.
895%
896*/
897static Image *ReadMGKImage(const ImageInfo *image_info,
898 ExceptionInfo *exception)
899{
900 char
901 buffer[MaxTextExtent];
902
903 Image
904 *image;
905
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]906 MagickBooleanType
907 status;
908
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]909 register PixelPacket
910 *q;
911
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]912 register size_t
913 x;
914
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]915 register unsigned char
916 *p;
917
918 ssize_t
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]919 count,
920 y;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]921
922 unsigned char
923 *pixels;
924
925 unsigned long
926 columns,
927 rows;
928
929 /*
930 Open image file.
931 */
932 assert(image_info != (const ImageInfo *) NULL);
933 assert(image_info-&gt;signature == MagickSignature);
934 if (image_info-&gt;debug != MagickFalse)
935 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info-&gt;filename);
936 assert(exception != (ExceptionInfo *) NULL);
937 assert(exception-&gt;signature == MagickSignature);
938 image=AcquireImage(image_info);
939 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
940 if (status == MagickFalse)
941 {
942 image=DestroyImageList(image);
943 return((Image *) NULL);
944 }
945 /*
946 Read MGK image.
947 */
948 (void) ReadBlobString(image,buffer); /* read magic number */
949 if (IsMGK(buffer,7) == MagickFalse)
950 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
951 (void) ReadBlobString(image,buffer);
952 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
953 if (count &lt;= 0)
954 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
955 do
956 {
957 /*
958 Initialize image structure.
959 */
960 image-&gt;columns=columns;
961 image-&gt;rows=rows;
962 image-&gt;depth=8;
963 if ((image_info-&gt;ping != MagickFalse) &amp;&amp; (image_info-&gt;number_scenes != 0))
964 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
965 break;
966 /*
967 Convert MGK raster image to pixel packets.
968 */
969 if (SetImageExtent(image,0,0) == MagickFalse)
970 {
971 InheritException(exception,&amp;image-&gt;exception);
972 return(DestroyImageList(image));
973 }
974 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,3UL*sizeof(*pixels));
975 if (pixels == (unsigned char *) NULL)
976 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]977 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]978 {
979 count=(ssize_t) ReadBlob(image,(size_t) (3*image-&gt;columns),pixels);
980 if (count != (ssize_t) (3*image-&gt;columns))
981 ThrowReaderException(CorruptImageError,"UnableToReadImageData");
982 p=pixels;
983 q=QueueAuthenticPixels(image,0,y,image-&gt;columns,1,exception);
984 if (q == (PixelPacket *) NULL)
985 break;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]986 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]987 {
988 q-&gt;red=ScaleCharToQuantum(*p++);
989 q-&gt;green=ScaleCharToQuantum(*p++);
990 q-&gt;blue=ScaleCharToQuantum(*p++);
991 q++;
992 }
993 if (SyncAuthenticPixels(image,exception) == MagickFalse)
994 break;
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]995 if ((image-&gt;previous == (Image *) NULL) &amp;&amp;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]996 (SetImageProgress(image,LoadImageTag,y,image&gt;>rows) == MagickFalse))
997 break;
998 }
999 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1000 if (EOFBlob(image) != MagickFalse)
1001 {
1002 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image-&gt;filename);
1003 break;
1004 }
1005 /*
1006 Proceed to next image.
1007 */
1008 if (image_info-&gt;number_scenes != 0)
1009 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
1010 break;
1011 *buffer='\0';
1012 (void) ReadBlobString(image,buffer);
1013 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
1014 if (count != 0)
1015 {
1016 /*
1017 Allocate next image structure.
1018 */
1019 AcquireNextImage(image_info,image);
1020 if (GetNextImageInList(image) == (Image *) NULL)
1021 {
1022 image=DestroyImageList(image);
1023 return((Image *) NULL);
1024 }
1025 image=SyncNextImageInList(image);
1026 status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image));
1027 if (status == MagickFalse)
1028 break;
1029 }
1030 } while (count != 0);
1031 (void) CloseBlob(image);
1032 return(GetFirstImageInList(image));
1033}
1034
1035/*
1036%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1037% %
1038% %
1039% %
1040% R e g i s t e r M G K I m a g e %
1041% %
1042% %
1043% %
1044%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1045%
1046% RegisterMGKImage() adds attributes for the MGK image format to
1047% the list of supported formats. The attributes include the image format
1048% tag, a method to read and/or write the format, whether the format
1049% supports the saving of more than one frame to the same file or blob,
1050% whether the format supports native in-memory I/O, and a brief
1051% description of the format.
1052%
1053% The format of the RegisterMGKImage method is:
1054%
1055% unsigned long RegisterMGKImage(void)
1056%
1057*/
1058ModuleExport unsigned long RegisterMGKImage(void)
1059{
1060 MagickInfo
1061 *entry;
1062
1063 entry=SetMagickInfo("MGK");
1064 entry-&gt;decoder=(DecodeImageHandler *) ReadMGKImage;
1065 entry-&gt;encoder=(EncodeImageHandler *) WriteMGKImage;
1066 entry-&gt;magick=(IsImageFormatHandler *) IsMGK;
1067 entry-&gt;description=ConstantString("MGK");
1068 entry-&gt;module=ConstantString("MGK");
1069 (void) RegisterMagickInfo(entry);
1070 return(MagickImageCoderSignature);
1071}
1072
1073/*
1074%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1075% %
1076% %
1077% %
1078% U n r e g i s t e r M G K I m a g e %
1079% %
1080% %
1081% %
1082%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1083%
1084% UnregisterMGKImage() removes format registrations made by the
1085% MGK module from the list of supported formats.
1086%
1087% The format of the UnregisterMGKImage method is:
1088%
1089% UnregisterMGKImage(void)
1090%
1091*/
1092ModuleExport void UnregisterMGKImage(void)
1093{
1094 (void) UnregisterMagickInfo("MGK");
1095}
1096
1097/*
1098%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1099% %
1100% %
1101% %
1102% W r i t e M G K I m a g e %
1103% %
1104% %
1105% %
1106%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1107%
1108% WriteMGKImage() writes an image to a file in red, green, and blue
1109% MGK rasterfile format.
1110%
1111% The format of the WriteMGKImage method is:
1112%
1113% MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1114%
1115% A description of each parameter follows.
1116%
1117% o image_info: the image info.
1118%
1119% o image: The image.
1120%
1121*/
1122static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
1123{
1124 char
1125 buffer[MaxTextExtent];
1126
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1127 MagickBooleanType
1128 status;
1129
1130 MagickOffsetType
1131 scene;
1132
1133 register const PixelPacket
1134 *p;
1135
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1136 register ssize_t
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1137 x;
1138
1139 register unsigned char
1140 *q;
1141
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1142 ssize_t
1143 y;
1144
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1145 unsigned char
1146 *pixels;
1147
1148 /*
1149 Open output image file.
1150 */
1151 assert(image_info != (const ImageInfo *) NULL);
1152 assert(image_info-&gt;signature == MagickSignature);
1153 assert(image != (Image *) NULL);
1154 assert(image-&gt;signature == MagickSignature);
1155 if (image-&gt;debug != MagickFalse)
1156 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image-&gt;filename);
1157 status=OpenBlob(image_info,image,WriteBinaryBlobMode,&amp;image-&gt;exception);
1158 if (status == MagickFalse)
1159 return(status);
1160 scene=0;
1161 do
1162 {
1163 /*
1164 Allocate memory for pixels.
1165 */
1166 if (image-&gt;colorspace != RGBColorspace)
1167 (void) SetImageColorspace(image,RGBColorspace);
1168 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,
1169 3UL*sizeof(*pixels));
1170 if (pixels == (unsigned char *) NULL)
1171 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
1172 /*
1173 Initialize raster file header.
1174 */
1175 (void) WriteBlobString(image,"id=mgk\n");
1176 (void) FormatMagickString(buffer,MaxTextExtent,"%lu %lu\n",
1177 image-&gt;columns,image-&gt;rows);
1178 (void) WriteBlobString(image,buffer);
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1179 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1180 {
1181 p=GetVirtualPixels(image,0,y,image-&gt;columns,1,&amp;image-&gt;exception);
1182 if (p == (const PixelPacket *) NULL)
1183 break;
1184 q=pixels;
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1185 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1186 {
1187 *q++=ScaleQuantumToChar(p-&gt;red);
1188 *q++=ScaleQuantumToChar(p-&gt;green);
1189 *q++=ScaleQuantumToChar(p-&gt;blue);
1190 p++;
1191 }
1192 (void) WriteBlob(image,(size_t) (q-pixels),pixels);
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1193 if ((image-&gt;previous == (Image *) NULL) &amp;&amp;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1194 (SetImageProgress(image,SaveImageTag,y,image-&gt;rows) == MagickFalse))
1195 break;
1196 }
1197 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1198 if (GetNextImageInList(image) == (Image *) NULL)
1199 break;
1200 image=SyncNextImageInList(image);
1201 status=SetImageProgress(image,SaveImagesTag,scene,
1202 GetImageListLength(image));
1203 if (status == MagickFalse)
1204 break;
1205 scene++;
1206 } while (image_info-&gt;adjoin != MagickFalse);
1207 (void) CloseBlob(image);
1208 return(MagickTrue);
1209}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1210</div>
1211
1212<p>To invoke the custom coder from the command line, use these commands:</p>
1213
1214<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert logo: logo.mgk</span><span class='crtout'></span><span class="crtprompt"> $magick&gt; </span><span class='crtin'>display logo.mgk</span></p>
1215<p>We provide the <a href="ftp://ftp.imagemagick.org/pub/ImageMagick/kits/MagickCoderKit-1.0.0.tar.gz">Magick Coder Kit</a> to help you get started writing your own custom coder.</p>
1216
1217</div>
1218
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1219<h2><a id="filters"></a>Custom Image Filters</h2>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1220<div class="doc-section">
1221
1222<p>ImageMagick provides a convenient mechanism for adding your own custom image processing algorithms. We call these image filters and they are invoked from the command line with the <a href="../www/command-line-options.html#process">-process</a> option or from the MagickCore API method <a href="../www/api/module.html#ExecuteModuleProcess">ExecuteModuleProcess()</a>.</p>
1223
1224<p>Here is a listing of a sample <a href="../www/source/analyze.c">custom image filter</a>. It computes a few statistics such as the pixel brightness and saturation mean and standard-deviation.</p>
1225
1226<div class="viewport">
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1227#include &lt;stdio.h&gt;
1228#include &lt;stdlib.h&gt;
1229#include &lt;string.h&gt;
1230#include &lt;time.h&gt;
1231#include &lt;assert.h&gt;
1232#include &lt;math.h&gt;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1233#include "magick/MagickCore.h"
cristydcca3fa2010-12-29 21:50:07 +0000[diff] [blame]1234
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1235/*
1236%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1237% %
1238% %
1239% %
1240% a n a l y z e I m a g e %
1241% %
1242% %
1243% %
1244%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1245%
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1246% analyzeImage() computes the brightness and saturation mean, standard
cristy52923442011-01-15 22:54:31 +0000[diff] [blame]1247% deviation, kurtosis and skewness and stores these values as attributes
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1248% of the image.
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1249%
1250% The format of the analyzeImage method is:
1251%
cristy178edaf2011-01-23 03:42:39 +0000[diff] [blame]1252% size_t analyzeImage(Image *images,const int argc,char **argv,
1253% ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1254%
1255% A description of each parameter follows:
1256%
1257% o image: the address of a structure of type Image.
1258%
1259% o argc: Specifies a pointer to an integer describing the number of
1260% elements in the argument vector.
1261%
1262% o argv: Specifies a pointer to a text array containing the command line
1263% arguments.
1264%
1265% o exception: return any errors or warnings in this structure.
1266%
1267*/
cristy178edaf2011-01-23 03:42:39 +0000[diff] [blame]1268ModuleExport size_t analyzeImage(Image **images,const int argc,const char **argv,
1269 ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1270{
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1271 char
1272 text[MaxTextExtent];
1273
1274 double
1275 area,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1276 brightness,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1277 brightness_mean,
1278 brightness_standard_deviation,
1279 brightness_kurtosis,
1280 brightness_skewness,
1281 brightness_sum_x,
1282 brightness_sum_x2,
1283 brightness_sum_x3,
1284 brightness_sum_x4,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1285 hue,
1286 saturation,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1287 saturation_mean,
1288 saturation_standard_deviation,
1289 saturation_kurtosis,
1290 saturation_skewness,
1291 saturation_sum_x,
1292 saturation_sum_x2,
1293 saturation_sum_x3,
1294 saturation_sum_x4;
1295
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1296 Image
1297 *image;
1298
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1299 assert(images != (Image **) NULL);
1300 assert(*images != (Image *) NULL);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1301 assert((*images)-&gt;signature == MagickSignature);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1302 (void) argc;
1303 (void) argv;
1304 image=(*images);
1305 for ( ; image != (Image *) NULL; image=GetNextImageInList(image))
1306 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1307 CacheView
1308 *image_view;
1309
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1310 MagickBooleanType
1311 status;
1312
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1313 ssize_t
1314 y;
1315
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1316 brightness_sum_x=0.0;
1317 brightness_sum_x2=0.0;
1318 brightness_sum_x3=0.0;
1319 brightness_sum_x4=0.0;
1320 brightness_mean=0.0;
1321 brightness_standard_deviation=0.0;
1322 brightness_kurtosis=0.0;
1323 brightness_skewness=0.0;
1324 saturation_sum_x=0.0;
1325 saturation_sum_x2=0.0;
1326 saturation_sum_x3=0.0;
1327 saturation_sum_x4=0.0;
1328 saturation_mean=0.0;
1329 saturation_standard_deviation=0.0;
1330 saturation_kurtosis=0.0;
1331 saturation_skewness=0.0;
1332 area=0.0;
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1333 status=MagickTrue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1334 image_view=AcquireCacheView(image);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1335#if defined(MAGICKCORE_OPENMP_SUPPORT)
1336 #pragma omp parallel for schedule(dynamic,4) shared(status)
1337#endif
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1338 for (y=0; y &lt; (ssize_t) image-&gt;rows; y++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1339 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1340 register const PixelPacket
1341 *p;
1342
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1343 register ssize_t
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1344 x;
1345
1346 if (status == MagickFalse)
1347 continue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1348 p=GetCacheViewVirtualPixels(image_view,0,y,image-&gt;columns,1,exception);
1349 if (p == (const PixelPacket *) NULL)
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1350 {
1351 status=MagickFalse;
1352 continue;
1353 }
cristyde368992010-11-05 14:32:14 +0000[diff] [blame]1354 for (x=0; x &lt; (ssize_t) image-&gt;columns; x++)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1355 {
1356 ConvertRGBToHSB(p-&gt;red,p-&gt;green,p-&gt;blue,&amp;hue,&amp;saturation,&amp;brightness);
1357 brightness*=QuantumRange;
1358 brightness_sum_x+=brightness;
1359 brightness_sum_x2+=brightness*brightness;
1360 brightness_sum_x3+=brightness*brightness*brightness;
1361 brightness_sum_x4+=brightness*brightness*brightness*brightness;
1362 saturation*=QuantumRange;
1363 saturation_sum_x+=saturation;
1364 saturation_sum_x2+=saturation*saturation;
1365 saturation_sum_x3+=saturation*saturation*saturation;
1366 saturation_sum_x4+=saturation*saturation*saturation*saturation;
1367 area++;
1368 p++;
1369 }
1370 }
1371 image_view=DestroyCacheView(image_view);
1372 if (area &lt;= 0.0)
1373 break;
1374 brightness_mean=brightness_sum_x/area;
1375 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_mean);
1376 (void) SetImageProperty(image,"filter:brightness:mean",text);
1377 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/
1378 area*brightness_sum_x/area));
1379 (void) FormatMagickString(text,MaxTextExtent,"%g",
1380 brightness_standard_deviation);
1381 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text);
1382 if (brightness_standard_deviation != 0)
1383 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean*
1384 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean*
1385 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean*
1386 brightness_mean*brightness_mean)/(brightness_standard_deviation*
1387 brightness_standard_deviation*brightness_standard_deviation*
1388 brightness_standard_deviation)-3.0;
1389 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_kurtosis);
1390 (void) SetImageProperty(image,"filter:brightness:kurtosis",text);
1391 if (brightness_standard_deviation != 0)
1392 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean*
1393 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean*
1394 brightness_mean)/(brightness_standard_deviation*
1395 brightness_standard_deviation*brightness_standard_deviation);
1396 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_skewness);
1397 (void) SetImageProperty(image,"filter:brightness:skewness",text);
1398 saturation_mean=saturation_sum_x/area;
1399 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_mean);
1400 (void) SetImageProperty(image,"filter:saturation:mean",text);
1401 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/
1402 area*saturation_sum_x/area));
1403 (void) FormatMagickString(text,MaxTextExtent,"%g",
1404 saturation_standard_deviation);
1405 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text);
1406 if (saturation_standard_deviation != 0)
1407 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean*
1408 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean*
1409 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean*
1410 saturation_mean*saturation_mean)/(saturation_standard_deviation*
1411 saturation_standard_deviation*saturation_standard_deviation*
1412 saturation_standard_deviation)-3.0;
1413 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_kurtosis);
1414 (void) SetImageProperty(image,"filter:saturation:kurtosis",text);
1415 if (saturation_standard_deviation != 0)
1416 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean*
1417 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean*
1418 saturation_mean)/(saturation_standard_deviation*
1419 saturation_standard_deviation*saturation_standard_deviation);
1420 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_skewness);
1421 (void) SetImageProperty(image,"filter:saturation:skewness",text);
1422 }
1423 return(MagickImageFilterSignature);
1424}
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1425</div>
1426
1427<p>To invoke the custom filter from the command line, use this command:</p>
1428
1429<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert logo: -process analyze -verbose info:</span><span class='crtout'>Image: logo: <br/>
1430 Format: LOGO (ImageMagick Logo) <br/>
1431 Class: PseudoClass <br/>
1432 Geometry: 640x480 <br/>
1433 ... <br/>
cristy178edaf2011-01-23 03:42:39 +0000[diff] [blame]1434 filter:brightness:kurtosis: 8.17947 <br/>
1435 filter:brightness:mean: 60632.1 <br/>
1436 filter:brightness:skewness: -2.97118 <br/>
1437 filter:brightness:standard-deviation: 13742.1 <br/>
1438 filter:saturation:kurtosis: 4.33554 <br/>
1439 filter:saturation:mean: 5951.55 <br/>
1440 filter:saturation:skewness: 2.42848 <br/>
1441 filter:saturation:standard-deviation: 15575.9</span></p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1442
1443<p>We provide the <a href="ftp://ftp.imagemagick.org/pub/ImageMagick/kits/MagickFilterKit-1.0.0.tar.gz">Magick Filter Kit</a> to help you get started writing your own custom image filter.</p>
1444
1445</div>
cristy3eaa0ef2010-03-06 20:35:26 +0000[diff] [blame]1446
1447</div>
1448
1449<div id="linkbar">
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1457 <div class="footer">
cristy7e41fe82010-12-04 23:12:08 +0000[diff] [blame]1458 <span id="footer-west">&copy; 1999-2011 ImageMagick Studio LLC</span>
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